Since June 2006, “porcine high fever disease” epidemic situation broke out in pig farms and peasant households in many provinces of China. The applicant studied and found that Super-Virulent Variant Strain of Porcine Reproductive and Respiratory Syndrome Virus (Nsp2 1594th-1680th deletion variant strain) is the primary cause of “porcine high fever disease” epidemic situation and then isolated and identified the virus (Classification Name: Porcine Reproductive and Respiratory Syndrome Virus; Latin Name Porcine Reproductive and Respiratory Syndrome Virus, PRRSV; Deposit Institution China Microbiological Spawn Deposit Management Committee General Microbiological Culture Collection Center (CGMCC); Deposit Date: Mar. 9, 2007; Deposit Nos.: CGMCC No. 1964).
Porcine Reproductive and Respiratory Syndrome caused by Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a disease with clinical features such as fever and abortion of sows, increased piglet mortality before and after weaning, and respiratory disorder in different ages of pigs. In 2006 and 2007, Porcine Reproductive and Respiratory Syndrome Virus Super-Virulent Variant Strain (Nsp2 1594th-1680th deletion variant strain), which has significantly increased pathogenicity on pigs and incurred heavy losses to pig farmers, is pandemic in China.
Since all currently available PRRSV Vaccines are not prepared in connection with the above variant strain, they can not generate protection against said variant strain. To some extent, the Inactivated Vaccine for approval at the present stage may resist the attack of PRRSV Super-Virulent Variant Strains (all inactivated Vaccines are prepared with no Super-Virulent variant strain, protective effects differ in different manufactures). In a view of the theoretic analysis, there is a need to develop a vaccine specifically aimed at Porcine Reproductive and Respiratory Syndrome Virus Super-Virulent Variant Strain (Nsp2 1594th-1680th deletion variant strain).
There are some defects in determining the efficacy of currently available PRRSV Vaccines. For example, since pathogenicity of the variant strain used (VR2332 standard variant strain) on pigs is not strong enough to lead to significant pathogenesis and death of pigs, it is difficult to evaluate the efficacy of PRRSV Vaccine based on immunity challenge protective test using the said standard strain.